In a modern automotive vehicle, the engine is equipped with fuel injectors that spray precise quantities of fuel into the air stream flowing through a manifold to the combustion chambers. The fuel is distributed to the injectors through a fuel rail mounted on the engine. A computer controller calculates the precise quantity of fuel and the opening time required by the fuel injector to release the precise quantity. The opening time is dependent upon the pressure drop across the injector, that is, the difference in pressure between the fuel pressure within the fuel rail and the air pressure within the manifold. The typical fuel system comprises a fuel pump located within a fuel tank and connected to the fuel rail through a fuel line. In an electronic returnless fuel system, a sensor is mounted in the fuel line or the fuel rail and provides an electrical signal to the controller that is indicative of fuel pressure. The controller utilizes the pressure signal in regulating the duty cycle of the fuel pump to maintain a desired fuel pressure. As a result, the system provides a predetermined fuel pressure for purposes of calculating the injector pressure drop.
Mechanical returnless fuel systems are known that include a pressure regulator coupled to the fuel line. The regulator opens to discharge fuel to the fuel supply to thereby relieve excess pressure within the fuel line. In a conventional mechanical returnless fuel system, the pressure regulator comprises a diaphragm biased by a spring and designed to maintain a substantially constant fuel pressure over a range of fuel flow rates typical of engine operation. As a result, the diaphragm regulator provides a constant fuel pressure that is relied upon by the controller for purposes of calculating the pressure drop across the injectors and thus the injector opening time. However, the diaphragm regulator requires a complex design and adds significantly to the cost of the system.
U.S. Pat. No. 6,953,026 issued Oct. 11, 2005 describes a pressure regulating valve for use in a mechanical returnless fuel system. Valve is a relatively less expensive design and produces a fuel pressure that is not constant, but rather is linearly proportional to the fuel flow rate.
Therefore, a need exists for a mechanical returnless fuel system wherein fuel pressure in the fuel line is subject to variation, and wherein the controller is able to determine a fuel pressure based upon pump operating conditions and without requiring an in-line fuel pressure sensor.